U.S. patent number 4,707,996 [Application Number 06/829,412] was granted by the patent office on 1987-11-24 for chemically assisted mechanical refrigeration process.
Invention is credited to Arnold R. Vobach.
United States Patent |
4,707,996 |
Vobach |
November 24, 1987 |
**Please see images for:
( Certificate of Correction ) ** |
Chemically assisted mechanical refrigeration process
Abstract
There is provided a chemically assisted mechanical refrigeration
process including the steps of: mechanically compressing a
refrigerant stream which includes vaporized refrigerant; contacting
the refrigerant with a solvent in a mixer (11) at a pressure
sufficient to promote substantial dissolving of the refrigerant in
the solvent in the mixer (11) to form a refrigerant-solvent
solution while concurrently placing the solution in heat exchange
relation with a working medium to transfer energy to the working
medium, said refrigerant-solvent solution exhibiting a negative
deviation from Raoult's Law; reducing the pressure over the
refrigerant-solvent solution in an evaporator (10) to allow the
refrigerant to vaporize and substantially separate from the solvent
while concurrently placing the evolving refrigerant-solvent
solution in heat exchange relation with a working medium to remove
energy from the working medium to thereby form a refrigerant stream
and a solvent stream; and passing the solvent and refrigerant
stream from the evaporator.
Inventors: |
Vobach; Arnold R. (Spring,
TX) |
Family
ID: |
27065598 |
Appl.
No.: |
06/829,412 |
Filed: |
February 13, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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763912 |
Aug 8, 1985 |
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537724 |
Sep 29, 1983 |
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363011 |
Mar 29, 1982 |
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Current U.S.
Class: |
62/114;
62/502 |
Current CPC
Class: |
F25B
25/02 (20130101); F02B 2075/027 (20130101) |
Current International
Class: |
F25B
25/02 (20060101); F25B 25/00 (20060101); F02B
75/02 (20060101); F25B 001/00 () |
Field of
Search: |
;62/114,117,476,335,525,502,112,101,115 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bennet; Henry A.
Attorney, Agent or Firm: Arnold, White & Durkee
Government Interests
The U.S. government has rights in this invention pursuant to
Department of Energy Grant No. DE-FG-46-81R 612081.
Parent Case Text
This application is a Continuation-in-Part of application Ser. No.
763,912 filed Aug. 8, 1985 which is a continuation of application
Ser. No. 537,724 filed Sept. 29, 1983 which is a
continuation-in-part of application Ser. No. 363,011 filed Mar. 29,
1982, all now abandoned.
Claims
What is claimed is:
1. A chemically assisted mechanical refrigeration process
comprising the steps of:
mechanically comprising a refrigerant stream comprising vaporized
refrigerant;
contacting the refrigerant with a solvent in a mixer at a pressure
sufficient to promote substantial dissolving of the refrigerant in
the solvent in the mixer to form a refrigerant-solvent solution
while concurrently placing the solution in heat exchange relation
with a working medium to transfer energy to the working medium,
said refrigerant-solvent solution exhibiting a negative deviation
from Raoult's Law;
reducing the pressure over the refrigerant-solvent-solution in an
evaporator to allow the refrigerant to vaporize and substantially
separate from the solvent while concurrently placing the evolving
refrigerant-solvent solution in heat exchange relation with a
working medium to remove energy from the working medium to thereby
form a refrigerant stream and a solvent stream;
passing the solvent and refrigerant stream from the evaporator;
and
placing the solvent stream leaving the evaporator in heat exchange
relation in an economizing zone with the refrigerant-solvent
solution leaving the mixer.
2. A process according to claim 1 wherein the solvent stream
leaving the evaporator includes a portion of dissolved refrigerant
and the solvent stream is placed in fluid communication with the
refrigerant stream leaving the evaporator in the economizing zone
to thereby allow mass transfer of gaseous refrigerant from the
solvent stream to the refrigerant stream and so facilitates heat
transfer in the economizing zone prior to ultimate passage of the
solvent and refrigerant streams to the mixer.
3. A process according to claim 2 wherein the solvent and
refrigerant streams are mechanically compressed together prior to
passage to the mixer.
4. A chemically assisted mechanical refrigeration process
comprising the steps of:
mechanically compressing a refrigerant stream comprising vaporized
refrigerant;
contacting the refrigerant with a solvent in a mixer at a pressure
sufficient to promote substantial dissolving of the refrigerant in
the solvent in the mixer to form a refrigerant-solvent solution
while concurrently placing the solution in heat exchange relation
with a working medium to transfer energy to the working medium,
said refrigerant-solvent solution exhibiting a negative deviation
from Raoult's Law;
reducing the pressure over the refrigerant-solvent-solution in an
evaporator to allow the refrigerant to vaporize and substantially
separate from the solvent while concurrently placing the evolving
refrigerant-solvent solution in heat exchange relation with a
working medium to remove energy from the working medium to thereby
form a refrigerant stream and a solvent stream;
passing the solvent and refrigerant stream from the evaporator;
and
placing the solvent leaving the evaporator in heat exchange
relation in an economizing zone with the refrigerant-solvent
solution leaving the mixer while passing a portion of the
compressed refrigerant directly into the refrigerant-solvent
solution passing to the evaporator.
5. A chemically assisted mechanical refrigeration process
comprising the steps of:
mechanically compressing a refrigerant stream comprising vaporized
refrigerant;
contacting the refrigerant with a solvent in a mixer at a pressure
sufficient to promote substantially dissolving of the refrigerant
in the solvent in the mixer to form a refrigerant-solvent solution
while concurrently placing the solution in heat exchange relation
with a working medium to transfer energy to the working medium,
said refrigerant-solvent solution exhibiting a negative deviation
from Raoult's Law;
reducing the pressure over the refrigerant-solvent-solution in an
evaporator to allow the refrigerant to vaporize and substantially
separate from the solvent while conurrently placing the evolving
refrigerant-solvent solution in heat exchange relation with a
working medium to remove energy from the working medium to thereby
form a refrigerant stream and a solvent stream;
passing the solvent and refrigerant stream from the evaporator;
and
wherein a portion of the refrigerant is passed to a
generator-absorber pair prior to entering the mixer.
6. A chemically assisted mechanical refrigeration process
comprising the steps of:
passing a stream of solution comprising a solvent and a liquified
refrigerant to an evaporator, said refrigerant and solvent having a
negative deviation from Raoult's Law when in combination;
reducing the pressure over the solution to allow refrigerant to
vaporize and separate from the solvent while concurrently placing
the evolving refrigerant and solvent in heat exchange relation with
a working medium to remove energy from the working medium and
thereby form a solvent stream and a refrigerant stream comprising
gaseous refrigerant leaving the evaporator;
passing the solvent stream leaving the evaporator in heat exchange
relation with the solution stream passing to the evaporator in an
economizing zone so as to cause transfer of heat between the
solvent stream and the solution, said heat transfer being
facilitated by the mass transfer of gaseous refrigerant in relation
to one or more of the streams passing through the economizing zone;
and
contacting the refrigerant stream and solvent stream in a mixing
zone comprising a mixer at a pressure sufficient to promote
substantial dissolving of the refrigerant in the solvent to form
the stream of solution for passage to the evaporator, while
concurrently placing the mixer in heat exchange relation with a
working medium to remove energy from the mixer.
7. A process according to claim 6 wherein the refrigerant stream is
mechanically compressed separately from the solvent stream prior to
passing the refrigerant to the mixer.
8. A process according to claim 6 wherein the solvent stream
leaving the evaporator includes a material portion of dissolved
refrigerant and the solvent stream is placed in fluid communication
with the refrigerant stream leaving the evaporator to accomplish
mass transfer of gaseous refrigerant from the solvent stream to the
refrigerant stream and so facilitate heat transfer in the
economizing zone prior to passage of the solvent and refrigerant
streams to the mixing zone.
9. A process according to claim 8 wherein the mixing zone further
comprises a joint compressing zone wherein the refrigerant and
solvent streams are brought into contact with each other and the
pressure on the refrigerant and solvent is raised sufficiently to
facilitate dissolving of the refrigerant in the solvent in the
mixer.
10. A process according to claim 9 wherein the refrigerant and
solvent streams are brought into contact in the compressing zone to
form a combined solvent-refrigerant stream and wherein the process
comprises the further step of placing the stream of solution and
the combined solvent-placing refrigerant stream passing to the
mixer in heat exchange relationship with each other prior to
passage of the stream of solution through the economizing zone.
11. A process according to claim 10 wherein the temperature of the
combined solvent-refrigerant stream approaches the temperature of
the mixer just prior to entering the mixer.
12. A process according to claim 6 wherein the mass transfer of
gaseous refrigerant is accomplished by passing a portion of the
refrigerant stream leaving the evaporator under pressure to the
stream of solution in the economizing zone, whereby the percentage
of refrigerant in the stream of solution is increased.
13. A chemically assisted mechanical refrigeration process
comprising the steps of:
passing a stream of solution comprising a solvent and a liquified
refrigerant to an evaporator, said refrigerant and solvent having a
negative deviation from Raoult's Law when in combination;
reducing the pressure over the solution to allow refrigerant to
vaporize and separate from the solvent while concurrently placing
the evolving refrigerant and solvent in heat exchange relation with
a working medium to remove energy from the working medium and
thereby form a solvent stream and a refrigerant stream comprising
gaseous refrigerant with both streams leaving the evaporator;
passing the solvent stream leaving the evaporator in heat exchange
relation with the solution stream passing to the evaporator in an
economizing zone so as to cause transfer of heat between the
solvent stream and the solution while concurrently placing the
solvent and refrigerant streams in fluid communication so as to
accomplish mass transfer of gaseous refrigerant from the solvent
stream to the refrigerant stream and so facilitate heat transfer in
the economizing zone between the solvent and solution streams;
contacting the solvent and the refrigerant streams in a joint
compression zone while raising the pressure over both streams to
form a combined solvent-refrigerant stream;
passing the combined solvent-refrigerant stream to a mixer while
maintaining a pressure sufficient to promote substantial dissolving
of the refrigerant in the solvent to form the stream of solution
for passage to the evaporator, while concurrently placing the mixer
in heat exchange relation with a working medium to remove energy
from the mixer.
14. A process according to claim 13 further comprising the step of
placing the solution and the combined solvent-refrigerant stream in
heat exchange relation with each other prior to passage of the
stream of solution through the economizing zone.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to refrigeration and more
particularly to a new and improved chemically assisted mechanical
refrigeration cycle.
The typical mechanical refrigeration system employs a mechanical
compressor to raise the pressure and to condense a gaseous
refrigerant, which thereafter absorbs its heat of vaporization.
Thus, the typical vapor compression cycle uses an evaporator in
which a liquid refrigerant, such as Freon-12, boils at a low
pressure to produce cooling; a compressor to raise the pressure of
the gaseous refrigerant after it leaves the evaporator; a
condenser, in which the refrigerant condenses and discharges its
heat to the environment; and an expansion valve through which the
liquid refrigerant leaving the condenser expands from the
high-pressure level in the condenser to the low pressure level in
the evaporator.
Much effort has been expended over the past few decades in
developing refrigeration systems which utilize low grade energy
sources, such as solar energy, without the need for compressors or
pumps. Much of this effort has been directed to the so-called
absorption cycle, which accomplishes compression by using a
secondary fluid as a solvent to absorb a refrigerant gas. A typical
absorption system includes a condenser, expansion valve and
evaporator, as does the vapor compression cycle. However, the
compressor is replaced by an absorber-generator pair. Lithium
bromide-water or water-ammonia are typical of the
solvent-refrigerant mixtures used.
The resorption cycle has also been studied. Introduced in the
earlier half of this century, the resorption cycle is similar in
operation to the absorption cycle. However, a resorber replaces the
condenser and the vapor is absorbed by a special weak solution
while condensing. This solution is then circulated to the
evaporator where the refrigerant boils and the heats of
disassociation and vaporization produce the refrigerating
effect.
Although the majority of prior systems avoid the use of compressors
when using a solvent-refrigerant combination, a few processes have
employed a solvent-refrigerant pair with a compressor in the
system. The system and method described in U.S. Pat. No. 4,037,426
is illustrative. There the gaseous refrigerant is compressed and
then mixed with liquid solvent. Thereafter, the mixture is cooled
in a heat exchanger and then passed to a decanter, where the
heavier liquid fraction is separated from the lighter liquid
refrigerant. The liquid refrigerant then passes to a zone of low
pressure where it is vaporized to absorb heat from a working fluid.
Systems or methods disclosed in U.S. Pat. Nos. 3,277,659 and
4,199,961 provide other examples of compressor type systems.
These and other prior systems suffer from one or more of several
limitations. For example, prior systems fail to take advantage of
both the heat of vaporization and the heat of dilution to
ultimately cool a working medium in a compression type cycle.
Additionally, prior systems utilizing a compressor require a heavy
duty compressor capable of sustaining relatively high compression
ratios. Other systems operate at comparatively high pressures which
require heavier duty components. Still, other systems have
relatively inefficient heat transfer mechanics. Yet other systems
fail to allow auxiliary heat exchange between refrigerant-solvent
and solvent without decreasing the density of the flow to the
compressor while other systems fail to provide sensible heat
transfer in an auxiliary heat exchange between refrigerant-solvent
and solvent. Still other systems fail to provide secondary
evolution of gaseous refrigerant from the solvent after the solvent
leaves the evaporator to facilitate overall efficiency. These and
other problems encountered by the prior systems are substantially
reduced, if not eliminated, by the present invention.
SUMMARY OF THE INVENTION
There is provided a chemically assisted mechanical refrigeration
process using a refrigerant and a solvent having a negative
deviation from Raoult's Law when in combination with each other. A
stream of solution including the solvent and a liquified
refrigerant is passed to an evaporator. The pressure over the
solution is then reduced to allow refrigerant to vaporize and
separate from the solvent. Concurrently therewith, the evolving
refrigerant and solvent are placed in heat exchange relation with a
working medium to remove energy from the working medium. A solvent
stream and a refrigerant stream including gaseous refrigerant are
formed and leave the evaporator. Thereafter, the refrigerant stream
undergoes mechanical compression and the refrigerant stream and
solvent stream are contacted at a pressure sufficient to promote
substantial dissolving of the refrigerant and the solvent. A stream
of solution is thus formed for passage to the evaporator. As the
refrigerant and solvent are in heat exchange relation with the
working medium for at least a portion of the time they are in
contact and mixing, energy is removed therefrom.
In one embodiment, the solvent stream leaving the evaporator is
preferably passed in heat exchange relation with the solution
stream passing to the evaporator. This occurs in an economizing
zone so as to cause transfer of heat between the solvent stream and
the solution stream.
Such heat transfer may be facilitated by the mass transfer of
gaseous refrigerant in relation to one or more of the streams
passing through the economizing zone. For example, in one
embodiment the solvent stream leaving the evaporator includes a
material portion of the dissolved refrigerant. The solvent stream
is placed in fluid communication with the refrigerant stream
leaving the evaporator to accomplish mass transfer of gaseous
refrigerant from the solvent stream to the refrigerant stream. This
in turn facilitates heat transfer in the economizing zone prior to
passage of the solvent stream and refrigerant stream to the mixing
zone.
In a modification of this embodiment, a mixing zone may be provided
including a mixer and a joint compression or compressing zone. In
the joint compression zone, the refrigerant and solvent stream are
brought into contact with each other and the pressure on the
refrigerant-solvent is raised sufficiently to facilitate dissolving
of the refrigerant in the solvent in the mixer.
In another modification of this embodiment, a mixing zone may be
provided, including a mixer, a liquid-pumping zone and a
gas-compressing zone. In the liquid-pumping zone, the pressure on
the liquid solvent stream is raised sufficiently to facilitate
dissolving of the refrigerant in the solvent in the mixer. In the
gas-compressing zone, the pressure on the gaseous refrigerant is
likewise raised sufficiently to facilitate dissolving of the
refrigerant in the solvent in the mixer. Furthermore, the solvent
stream, either before or after passing through the pumping zone, is
passed in heat exchange relationship, but not in fluid
communication, with the refrigerant stream in the gas-compressing
zone.
The heat exchange between the liquid solvent stream and the gaseous
refrigerant stream in the gas-compressing zone may be accomplished
by a solvent stream cooling jacket around any of the various
compressors which may be used to compress the gaseous
refrigerant.
Where the refrigerant and solvent streams leaving the evaporator
are placed in fluid communication with each other to allow
evolution of gases from the solvent stream, and the two streams
thereafter pass to a joint compressing zone including a single
compressor; the compressor may be a rotary compressor, centrifugal
compressor or rotary screw compressor.
In still a further modification, refrigerant and solvent streams
leaving the evaporator may be brought into contact in the
compressing zone to form a combined solvent-refrigerant stream. The
solvent-refrigerant stream leaving the compressing zone and passing
to the mixer may then be placed in heat exchange relation with the
stream of solution leaving the mixer prior to passage of the stream
of solution to the economizing zone. It is believed that the
temperature of the combined solvent-refrigerant stream preferably
approaches the temperature of the mixer just prior to entering the
mixer.
In another embodiment the mass transfer of gaseous refrigerant is
accomplished by passing a portion of the refrigerant stream leaving
the compression zone to the stream of solution in the economizing
zone, whereby the percentage of refrigerant in the solution stream
is increased.
In a more detailed embodiment, there may be provided a chemically
assisted mechanical refrigeration process including several steps.
A stream of solution including a solvent and a liquified
refrigerant is passed to an evaporator. The refrigerant and solvent
have a negative deviation from Raoult's Law when in combination.
The pressure is then reduced over the solution to allow refrigerant
to vaporize and separate from the solvent while concurrently
therewith the evolving refrigerant and solvent are put in heat
exchange relation with a working medium to remove energy from the
working medium and thereby form a solvent stream and a refrigerant
stream leaving the evaporator. The refrigerant stream includes
gaseous refrigerant. The solvent stream leaving the evaporator is
then passed in heat exchange relation with the solution stream
passing to the evaporator in an economizing zone so as to cause
transfer of heat between the solvent stream and the solution.
Concurrently therewith, the solvent and refrigerant streams are put
in fluid communication with each other so as to accomplish mass
transfer of gaseous refrigerant from the solvent stream to the
refrigerant stream and so facilitate heat transfer in the
economizing zone between the solvent and solution streams. The
solvent and refrigerant streams are subsequently contacted in a
joint compressing zone where the pressure over both streams is
raised to form a combined solvent-refrigerant stream. The combined
solvent-refrigerant stream is then passed to a mixer under a
pressure sufficient to promote substantial dissolving of the
refrigerant in the solvent to form the stream of solution for
passage to the evaporator. As the mixer is in heat exchange
relation with a working medium, energy is removed from the
mixer.
In another more detailed embodiment, there may be provided a
chemically assisted mechanical refrigeration process including
several steps. A stream of solution including a solvent and a
liquified refrigerant is passed to an evaporator. The refrigerant
and solvent have a negative deviation from Raoult's Law when in
combination. The pressure is then reduced over the solution to
allow refrigerant to vaporize and separate from the solvent while
concurrently therewith the evolving refrigerant and solvent are put
in heat exchange relation with a working medium to remove energy
from the working medium and thereby form a solvent stream and a
refrigerant stream leaving the evaporator. The refrigerant stream
includes gaseous refrigerant. The solvent stream leaving the
evaporator is then passed in heat exchange relation with the
solution stream passing to the evaporator in an economizing zone so
as to cause transfer of heat between the solvent stream and the
solution. Concurrently therewith, the solvent and refrigerant
streams are put in fluid communication with each other so as to
accomplish mass transfer of gaseous refrigerant from the solvent
stream to the refrigerant stream and so facilitate heat transfer in
the economizing zone between the solvent and solution streams. The
solvent and refrigerant streams are subsequently separately
pressurized in liquid-pumping and gas-compressing zones, with the
solvent stream being put into heat exchange relation, but not in
contact, with the refrigerant in the gas-compressing zone. The
solvent and refrigerant streams are then passed to a mixer under a
common pressure sufficient to promote substantial dissolving of the
refrigerant in the solvent to form the stream of solution for
passage to the evaporator. As the mixer is in heat exchange
relation with a working medium, energy is removed from the
mixer.
Furthermore, in a still more detailed embodiment of the one
described immediately above, that portion of the solvent stream
passing from the evaporator to the mixer may be put in heat
exchange relation, either before or after passage through the
liquid-pumping zone, with the solution stream passing from the
mixer to the said economizing zone.
In another embodiment, the vaporized refrigerant may be compressed
by passing a high velocity liquid jet of solvent into the
refrigerant. A portion of the refrigerant may also be passed to a
generator-absorber pair prior to entering the mixer.
There is also provided in accordance with the present invention a
chemically assisted mechanical refrigeration apparatus including a
mechanical compressor for compressing a refrigerant and a mixing
zone including a mixer for receiving a solvent and the compressed
refrigerant at a pressure sufficient to promote substantial
solution of the refrigerant in the solvent and form a
solvent-refrigerant stream. There is also provided an evaporator
zone including or consisting of an evaporator for receiving the
refrigerant-solvent stream from the mixer and ultimately returning
the refrigerant to the mixer after allowing at least a substantial
portion of the refrigerant to separate from the solvent and absorb
heats of vaporization and dissolution from a working medium, which
medium is in heat exchange relation with the evolving
refrigerant-solvent.
There may also be provided an economizing zone for placing the
solvent passing from the evaporator zone to the mixing zone in heat
exchange relation with the refrig- erant-solvent stream passing
from the mixer to the evaporator zone. For example, a heat
exchanger including a conduit for passage of solvent and a surface
adjacent to the conduit for receiving a thin film of
solvent-refrigerant may be provided. There may also be provided an
injection mechanism for passing a portion of the compressed
refrigerant directly into solution with the refrigerant-solvent
stream after the mixture passes from the mixer as well as a heat
exchanger for placing the refrigerant-solvent stream leaving the
mixer in heat exchange relation with the solvent or both compressed
refrigerant and solvent entering the mixer.
Coils may be substantially immersed in liquid in the evaporator for
circulating the working medium or the evaporator may comprise a
shell and tube heat exchanger arrangement. In some embodiments, the
mechanical compressor may be a jet compressor adapted to use
solvent from the evaporator to compress the refrigerant leaving the
evaporator.
In a more detailed embodiment, there may be provided a chemically
assisted mechanical refrigeration apparatus including an evaporator
zone for receiving a refrigerant-solvent stream at a pressure
sufficient to allow the refrigerant to separate from the solvent
and absorb a substantial portion of the heats of vaporization and
dissolution of the solvent-refrigerant stream from a working medium
which is in heat exchange relation with the evolving
refrigerant-solvent combination. A compressor is provided and
adapted to accept a gaseous stream and a liquid stream and raise
the pressure of said streams upon combination. A solvent conduit
connects the evaporator and the compressor to allow passage of
solvent from the evaporator to the compressor. A refrigerant
conduit connects the evaporator and the compressor for passage of a
gaseous refrigerant from the evaporator to the compressor. The
refrigerant conduit is in fluid communication with the solvent
conduit such that the refrigerant conduit may receive gases
evolving from the solvent passing through the solvent conduit. A
solution conduit having one end connected to the mixer and the
other end connected to the evaporator is also provided. The
solution conduit is adapted to facilitate any reduction in pressure
between the mixer and the evaporator. An economizer is also
provided for placing the solvent conduit and the solution conduit
in heat exchange relation with each other.
In any case where refrigerant and solvent are contacted in the
compressor, the compressor may be a rotary compressor, centrifugal
compressor or rotary screw compressor.
In another more detailed embodiment, there may be provided a
chemically assisted mechanical refrigeration apparatus including an
evaporator zone for receiving a refrigerant-solvent stream at a
pressure sufficient to allow the refrigerant to separate from the
solvent and absorb a substantial portion of the heats of
vaporization and of dissolution of the solvent-refrigerant stream
from a working medium which is in heat exchange relation with the
evolving refrigerant-solvent combination. A compressor and a pump
are provided and adapted to accept a gaseous stream and a liquid
stream, respectively, and to raise the pressures of said streams. A
first solvent conduit connects the evaporator and the pump to allow
passage of solvent from the evaporator to the pump. This first
solvent conduit is adapted to permit heat exchange between the
solvent stream and the gaseous refrigerant stream in the
compressor. A first refrigerant conduit connects the evaporator and
the compressor for passage of a gaseous refrigerant from the
evaporator to the compressor. This first refrigerant conduit is in
fluid communication with said first solvent conduit such that this
first refrigerant conduit may receive gases evolving from the
solvent passing through said first solvent conduit. Second
refrigerant and solvent conduits conduct the refrigerant and
solvent streams from compressor and pump, respectively, to the
mixer. A solution conduit having one end connected to the mixer and
the other end connected to the evaporator is also provided. The
solution conduit is adapted to facilitate any reduction in pressure
between the mixer and the evaporator. An economizer is also
provided for placing said first solvent conduit and the solution
conduit in heat exchange relation with each other.
Another more detailed embodiment differs from the one immediately
preceding only in that the first solvent conduit between evaporator
and pump is not adapted for heat exchange at the compressor,
whereas the second solvent conduit connecting the pump and the
mixer is adapted for heat exchange relationship with the solution
conduit.
In all such cases where refrigerant and solvent are contacted in
the compressor, the compressor may be a rotary compressor,
centrifugal compressor or screw compressor.
Various embodiments will now be described by way of example with
respect to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a chemically assisted mechanical
refrigeration cycle;
FIG. 2 is a schematic view of another embodiment of the chemically
assisted mechanical refrigeration cycle;
FIG. 3 is a schematic view of an evaporator for use in the
embodiments shown in FIGS. 1, 2 and 4;
FIG. 4 is a schematic view of yet another embodiment of the present
invention; and
FIG. 5 is a schematic view of yet another embodiment of the present
invention.
There follows a detailed description of certain embodiments of the
present invention, including those presently preferred, in
conjunction with the foregoing drawings. This description is to be
taken by way of illustration rather than limitation.
DETAILED DESCRIPTION
Referring now to FIG. 1, there is shown a schematic view of a
chemically assisted mechanical refrigeration cycle. An appropriate
solvent-refrigerant stream preferably having the refrigerant
totally in solution is introduced into evaporator 10 from line 21.
As will hereinafter be more fully described, refrigerant vaporizes
and separates from solvent under the operating conditions in the
evaporator 10, such that heats of dissolution and vaporization are
transferred to a working medium, such as water, circulating in
conduit 22. A solvent stream leaves as a liquid and is pumped by
solvent pump 13 via line 19 to mixer-condenser 11, while a
refrigerant stream of vaporized refrigerant leaves the evaporator
via line 18 and through normally open valve 76 to be compressed in
compressor 12 before being transferred to mixer 11 via line 14.
Valves 71 and 74 are operated to prevent any flow from occurring in
lines 72 and 73, respectively. Similarly, valve 81 prevents flow
through line 82.
At the operating conditions of the mixer 11 the now compressed
refrigerant is dissolved into the solvent entering the mixer from
line 19. Heats of mixing and condensation are withdrawn from the
condenser-mixer 11 via a working medium in line 23. There is thus
formed a solvent-refrigerant stream.
The solvent-refrigerant stream passes via line 15 through expansion
valve 16 where it is reduced in pressure before entering evaporator
10 via line 21.
The evaporator-effervescer 10 is so constructed as to allow
substantial transfer of both the heat of vaporization and the heat
of disassociation from the working fluid circulating through line
22. As efficient heat transfer is promoted through the use of a
wetted heat transfer surface, the heat transfer surface may
preferably be wetted by the solvent with or without dissolved
refrigerant. Thus, in one embodiment the refrigerant-solvent stream
may be passed as a thin film over a heat transfer surface with
embedded coils containing the working fluid.
In another embodiment shown in FIG. 3 a working fluid, such as
chilled water, is passed via line 22 through the shell side of a
shell and tube type heat exchanger while the refrigerant-solvent
stream entering from line 21 passes through the tube side. The
refrigerant separates from the solvent in the tubes and both
solvent and refrigerant pass to a liquid-vapor separator 31 where
the solvent and refrigerant are separated. The liquid-vapor
separator 31 may be equipped with a wire mesh 32 to catch entrained
droplets which collect below wire mesh 32. The solvent passes via
line 33 to pump 13 while the refrigerant passes via line 18 to
compressor 12.
In another embodiment, the conduit 22 is substantially immersed in
liquid in the evaporator. As the refrigerant-solvent stream enters
the evaporator the refrigerant substantially disassociates and
boils off from the solvent, thus cooling the working fluid. In such
an embodiment the evaporator may be similar in construction to a
shell and tube heat exchanger wherein the working medium circulates
through the tubes, which are substantially immersed in liquid.
Alternatively, the working medium may pass through a coil, which
passes through the lower portion of the evaporator and so is
substantially immersed in liquid. By way of example, the
refrigerant-solvent stream may circulate and undergo separation in
a single-tube coil of 1/2' diameter for a one to four ton apparatus
and then further separate in a liquid-vapor separator.
As would be known to one skilled in the art having the benefit of
this disclosure, the evaporator may comprise any one of several
modified heat exchangers or evaporators.
Where it is desirable to facilitate the separation of the vaporized
refrigerant from solvent an eliminator may be employed at the vapor
outlet of the evaporator if the vapor and liquid separate into two
streams in the evaporator. This may be particularly appropriate
when the refrigerant is passed separately from the solvent to a
mechanical compressor.
The compressor may be any one of several mechanical types.
Regardless of the type of compressor used, in keeping with the
spirit of the present invention, its operating cost should
generally be less than that of its counterpart in a typical vapor
compression refrigeration system for a given application. This is
possible due to the increased efficiency of the present system.
This increased efficiency over prior mechanical vapor compression
cycles is believed to result in part from the fact that the
solubility of the refrigerant in the solvent reduces the level of
required mechanical compression. The refrigerant need only be
pressurized sufficiently to dissolve in the solvent in the
condenser at the given operating conditions and concentrations.
There is believed to be little or no wasted compression of the
refrigerant to pressurize it sufficiently to condense at the
condenser temperature as in the usual vapor compression cycle.
Additionally, since the refrigerant is at a lower temperature as it
leaves the mixer than in the case of a pure refrigerant cycle, less
heat transfer is required and hence less working fluid need be
circulated to the mixer.
The compressor chosen may vary with operating conditions, the
refrigerant-solvent combination chosen or the application to which
the system is applied. For example, for the embodiments shown in
FIGS. 1 and 2, a centrifugal, rotary or screw compressor may be
preferred since the gas refrigerant passing through line 18 may
still have some entrained liquid despite the use of an eliminator
at the outlet of the evaporator 10. Alternately, for the embodiment
shown in FIG. 4 where the refrigerant and solvent streams leaving
the evaporator are placed in fluid communication with each other to
allow evolution of gases from the solvent stream, and the two
streams thereafter pass to a single compressor, the compressor may
be a rotary compressor, centrifugal compressor or rotary screw
compressor.
Where a solvent pump is to be used, as for example in the
embodiments set out in FIGS. 1 and 2, the solvent pump 13 may be
any type suitable to pump the liquid solvent to the mixer under the
operating conditions of the system. A centrifugal pump may be
preferred due to its simplicity, low first cost, uniform
nonpulsating flow, low maintenance expense, quiet operation and
adaptability to use with either a motor or a turbine drive. On the
other hand, a positive displacement pump such as a rotary, screw or
gear pump may be preferred.
Keeping in mind the difference in pressure between the evaporator
10 and the mixer 11, the mixer may be of a design similar to that
of the evaporator, such that the system may serve as a heater as
well as a refrigerator.
The refrigerant-solvent combination comprises at least two
constituents--a refrigerant and a solvent. The refrigerant and
solvent are chosen such that the refrigerant will separate as a gas
from the solvent under the operating conditions in the evaporator
while preferably absorbing substantial amounts of the heats of
demixing, dilution, or disassociation as well as vaporization.
Thus, a governing principle for the selection of a
refrigerant-solvent combination is that the refrigerant be highly
soluble in the solvent, such that the pair exhibits negative
deviations from Raoult's Law.
Examples of refrigerants which are believed to be suitable for use
in the present invention with appropriate solvents include
hydrocarbons such as methane, ethane, ethylene and propane;
halogenated hydrocarbons, such as refrigerants R20, R21, R22, R23,
R30, R32, R40, R41, R161 and R1132a; amines, including methylamine,
or gases used in certain refrigeration processes such as methyl
chloride, sulfur dioxide, ammonia, carbon monoxide and carbon
dioxide or any appropriate combinations of these.
The solvent constituent should be a substantially non-volatile
liquid at the operating conditions of the cycle or be at least such
when in solution with a portion of the refrigerant. Thus, the
solvent, for example, nitrous oxide, can be a gas at room
temperature.
It is believed that the solvent may be an ether, an ester, an
amide, an amine or polymeric derivatives of these, for example,
dimethyl formamide and dimethyl ether of tetraethylene glycol as
well as halogenated hydrocarbons, such as carbon tetrachloride and
dichlorethylene; or appropriate combinations of these. A
halogenated salt such as lithium bromide may also be a constituent
of the solvent.
Also believed to be suitable as solvents are methanol, ethanol,
acetone, chloroform and trichloroethane. Organic physical solvents
such as propylene carbonate and sulfolane or other organic liquids
containing combined oxygen may be used.
Relatively large deviations from Raoult's Law and hence relatively
large heats of mixing are obtained when one, or preferably both, of
the refrigerant and solvent molecules is polar. The excess
solubility is believed to be a consequence of either dipole-dipole
attraction (including hydrogen bonding) or induced dipole-dipole
attraction.
Alternatively, limited experimental data and calculations indicate
that certain combinations of refrigerant and solvent may not have a
satisfactory coefficient of performance. Thus, calculations on the
embodiment shown in FIG. 4 indicate that a combination of carbon
dioxide and 1,1,1-trichloroethane may not be very efficient. More
particularly, calculations generally paralleling those set out
below with respect to 1,1,1-trichloroethane and R22 with respect to
FIG. 4 resulted in a coefficient of performance of 1.83 for assumed
evaporator and mixer temperatures of 5.degree. F. (-15.00.degree.
C.) and 86.degree. F. (30.00.degree. C.), respectively, and 1.49
for assumed evaporator and mixer temperatures of 40.degree. F.
(4.44.degree. C.) and 110.degree. F. (43.33.degree. C.). This may
possibly be explained by the high critical temperatures and
pressures of carbon dioxide of 87.87.degree. F. (31.04.degree. C.)
and 1069.96 psia (7,377.11 kPa absolute), respectively.
It is believed that other chemical constituents may be added to the
basic pair for other purposes, including foaming, lubrication,
inhibition of corrosion, lowering of the freezing point, raising of
the boiling point or indication of leaks. However, such added
constituents should preferably be chosen so as not substantially to
detract from the heat of disassociation or vaporization produced in
the evaporator. Further, the constituents are preferably such as to
not detract from any negative deviations from Raoult's Law.
The comparative efficiency of the instant invention is illustrated
by reference to available data for a refrigerant-solvent pair
comprising CHClF.sub.2 (refrigerant 22) and dimethyl formamide
(DMF). According to an enthalpy-concentration diagram disclosed in
Jelinek, M., et al, Enthalpy--Concentration Diagram--A.S.H.R.A.E.
Trans., 84 (1978), Pt. II, pp. 60-67, herein incorporated by
reference, an R22-DMF solution is in equilibrium at 56.8 psig
(391.62 kPa gage) and 86.degree. F. (30.00.degree. C.) with a
weight distribution of 60% R.sub.22 and 40% DMF. If pressure is
reduced sufficiently, the R.sub.22 will boil out of the DMF,
absorbing a combined heat of vaporization and heat of mixing of
slightly more than 72 Btu/lb (167.36 J per kg). Alternatively, the
heat of mixing can be calculated from Equation (14) in Tyagi, K.P.,
Heat of Mixing--, Ind. Jnl. of Tech., 14 (1976), pp. 167-169,
herein incorporated by reference, to be 19.33 Btu/lb. (44.93 J per
kg), while the heat of vaporization of the R.sub.22 is 55.92
Btu/lb. (129.98 J per kg) of solution. Thus, the total heat
absorbed per pound of solution entering the evaporator is 75.25
Btu/lb. (174.91 J per kg), in close agreement with the
enthalpy-concentration diagram mentioned above.
Although it may be preferable that the refrigerant-solvent mixture
or combination be chosen such that a substantial amount of
refrigerant vaporizes from solution in the evaporator, this need
not always be the case. For example, a refrigerant with a
comparatively high heat of vaporization may be circulated in small
proportions relative to the amount of solvent when the
refrigerant-solvent leaving the mixer is placed in heat exchange
relation with the solvent leaving the evaporator, as shall
hereinafter be more fully described in conjunction with FIG. 2.
In an alternative embodiment, the solvent leaving the evaporator
can be passed through an economizer or auxiliary heat exchanger.
Unlike many prior systems, such as described in U.S. Pat. No.
3,277,659 issued to Sylvan, there is no need to directly heat the
suction vapor passing to the compressor, thus reducing its density
and increasing the volume of gas handled by the compressor.
One form of this embodiment is illustrated in FIG. 2. The operation
of this embodiment is similar to that of the embodiment shown in
FIG. 1. However, an economizer, which may be similar to a Baudelot
cooler, is employed. Additionally, valves 41 and 42 will generally
be closed unless the compressor is to be assisted by the
absorber-generator pair as shall hereinafter be more fully
described.
The refrigerant-solvent solution flows downward in a film over
surfaces in the economizer-heat exchanger 26. These surfaces are
chilled by cold solvent returning through conduit 24 from the
evaporator-effervescer 10. The cooling cascading
refrigerant-solvent may also be bathed in the atmosphere of still
cool refrigerant bled by valve 79 from the compressor outlet
through conduit 27. Consequently, the heat of condensation as well
as the heat of mixing of additional refrigerant absorbed by the
cooled refrigerant-solvent stream is transferred to the cold
solvent circulating through the economizer. Alternately, valve 79
may be closed and exchanger 26 operated only as a heat exchanger
without any mixing occurring therein.
In operation the compressor 12 pumps and compresses the refrigerant
gas and pumps the compressed gas through conduit 14, while valve 79
is opened and another portion of the compressed gas is pumped
through conduit 27. The compressed gas going to the mixer 11 is
mixed with the solvent and the refrigerant-solvent stream is
directed through conduit 15 to the economizer 26 and expansion
valve 16. The refrigerant-solvent is then directed to the
evaporator 10 as in FIG. 1. The solvent from the evaporator is
conducted via conduit 24 to the economizer 26 by the solvent pump
13 for recycling through the system. The compressor 12 draws or
sucks vaporized refrigerant through conduit 18 to complete the
cycle. The efficiency of the process may thus be enhanced through
use of an economizer to subcool the refrigerant-solvent and
increase the net refrigerating effect of the solution. Valve 79 may
be operated to regulate or prevent flow through line 27 such that a
specified portion or all of the compressed refrigerant passes to
condenser-mixer 11.
The compressed gas leaving the compressor 12, via conduit 14, may
also be put in heat exchange relation with the refrigerant-solvent
stream leaving mixer 11 to subcool the latter if the operating
temperature of the mixer 11 is above that of the compressed gas in
conduit 14. Thus, as shown in FIG. 1, valves 81 and 83, which are
normally closed, may be opened such that compressed refrigerant
passes via line 82 to heat exchanger 85 where it exchanges heat
with the solvent-refrigerant stream passing through line 15. The
compressed refrigerant then passes via line 84 to mixer 11 as
already described.
In a presently preferred embodiment, there may be provided a
chemically assisted mechanical refrigeration process including
several steps. The refrigerant and solvent have a negative
deviation from Raoult's Law when in combination. A stream of
solution including a solvent and a liquified refrigerant is passed
to an evaporator. The pressure is then reduced over the solution to
allow refrigerant to vaporize and separate from the solvent while
concurrently therewith the evolving refrigerant and solvent are put
in heat exchange relation with a working medium to remove energy
from the working medium and thereby form a solvent stream and a
refrigerant stream leaving the evaporator. The refrigerant stream
includes gaseous refrigerant. The solvent stream leaving the
evaporator is then passed in heat exchange relation with the
solution stream passing to the evaporator in an economizing zone so
as to cause transfer of heat between the solvent stream and the
solution. Concurrently therewith, the solvent and refrigerant
streams are put in fluid communication with each other so as to
accomplish mass transfer of gaseous refrigerant from the solvent
stream to the refrigerant stream and so facilitate heat transfer in
the economizing zone between the solvent and solution streams. The
solvent and refrigerant streams are subsequently contacted in a
joint compression zone where the pressure over both streams is
raised to form a combined solvent-refrigerant stream. The combined
solvent-refrigerant stream is then passed to a mixer under a
pressure sufficient to promote substantial dissolving of the
refrigerant in the solvent to form the stream of solution for
passage to the evaporator. As the mixer is in heat exchange
relation with a working medium, energy is removed from the
mixer.
Turning now to FIG. 4, there will be described a more specific
embodiment of a presently preferred embodiment. A solvent-liquified
refrigerant stream is passed via line 25 to evaporator 10. The
refrigerant and solvent of the solvent-liquified refrigerant stream
have a negative deviation from Raoult's Law and may be chosen from
a number of combinations of substances already described. By way of
example, a refrigerant-solvent combination of R.sub.22
-trichloroethane might be employed.
As essentially discussed in conjunction with the embodiments shown
in FIGS. 1 and 2, the pressure over the solvent-refrigerant stream
is reduced in the evaporator in order to allow refrigerant to
vaporize and separate from the solvent while concurrently placing
the evolving refrigerant and solvent in heat exchange relation with
the working medium to remove energy from the working medium. As a
result, there is formed a solvent stream which passes via line 24
and the refrigerant stream including gaseous refrigerant which
passes via line 18.
It is believed that the solvent stream passing via line 24 may
contain a material portion of refrigerant without hindering the
efficiency of the process. More particularly, the solvent stream
leaving the evaporator and passing via line 24 is placed in heat
exchange relation with the solvent-refrigerant stream passing to
the evaporator via lines 15 and 25. Further, the solvent stream in
line 24 is placed in fluid communication with the refrigerant
stream of line 18 such that gaseous refrigerant evolving from the
solvent stream 24 may pass via conduit 92 to refrigerant stream 18.
This evolution of gas tends to cool the solvent stream, thus
facilitating heat transfer in the economizer or economizing zone,
which in turn increases the temperature drop in the
solvent-refrigerant stream as it passes through the economizing
zone. Put another way, any inefficiencies in the evaporator caused
by a failure of the refrigerant to separate from the solvent are
believed diminished since the refrigerant is allowed to further
evolve from the solvent and the resulting change in energy is
transferred indirectly to the working medium passing through the
evaporator by virtue of the lowering of temperature of the
solvent-refrigerant stream as it enters the evaporator.
Both the solvent stream and the refrigerant stream are then brought
into contact in a joint compression zone as illustrated by
compressor 88 in FIG. 4. The compression of the refrigerant along
with the liquid in a joint compression zone such as compressor 88
is believed to provide several advantages. Thus, the liquid solvent
would generally have a higher heat capacity than the refrigerant
and generally act as a coolant in the compressor, thus reducing the
amount of work required to compress the refrigerant. Additionally,
a liquid solvent may be chosen which acts both as a sealant and
lubricant as well as a coolant. Thus, when a refrigerant gas is
compressed and the solvent pumped simultaneously by a single
compressor-pump, such as compressor 88 in the joint compression
zone, several advantages can accrue. For example, the solvent
provides internal cooling of the overall apparatus thus permitting
compression which is more polytropic than isentropic and hence
generally more economical. Additionally, it is believed that the
presence of the solvent in the compressor permits higher pressures
in the case of a centrifugal compressor, or serves as a lubricant
and sealant in case of a rotary compressor.
The resulting combined solvent-refrigerant stream flows via line 90
into mixer 11. As already substantially described with respect to
FIGS. 1 and 2, in the mixer 11 the combined solvent-refrigerant
stream is maintained at a pressure sufficient for the given
temperature to promote substantial dissolving of the refrigerant in
the solvent to form the stream of solution for passage to the
evaporator 10 via lines 15 and 25. Concurrently therewith, the
mixer is in heat exchange relation with a working medium which
removes energy or heat given off by the dissolving and condensing
refrigerant in the mixer 11.
The operation of the embodiment shown in FIG. 4 is further
highlighted by the various temperatures shown in the drawing, all
of which are in degrees Farenheit. These temperatures were
calculated based on the following presumptions. It is presumed that
a cycle using R.sub.22 as a refrigerant and 1,1,1-trichloroethane
(TCE) as a solvent was employed with an evaporator temperature of
40.degree. F. (4.44.degree. C.) and a mixer temperature of
110.degree. F. (43.33.degree. C.). Based on the resulting
calculations from heat balances, it is believed that the
theoretical coefficient of performance of the system would be 6.71,
which compares favorably with 5.75 for a pure R.sub.22 vapor
compression cycle generally used in prior art systems. (The
theoretical maximum coefficient of performance for a perfect
(Carnot) cycle is 7.14.)
Various data necessary to the calculations, vapor densities,
discharge temperatures of isentropic compression to determine
polytropic discharge temperatures and so forth were taken from
American Society of Heating, Refrigerating and Air Conditioning
Engineers, Thermophysical Properties of Refrigerants, 1976, and
American Society of Heating, Refrigerating and Air Conditioning
Engineers, Thermodynamic Properties of Refrigerants, 1980. Where
extrapolations had been made, it is believed that they were
generally made in the direction of conservative estimates with
respect to cycle performance.
Based on one pound of circulating mass, an R.sub.22 -TCE cycle with
an evaporator temperature of 40.degree. F., (4.44.degree. C.) and a
mixer temperature of 110.degree. F. (43.33.degree. C.), at
110.degree. F. (43.33.degree. C.) and 94.7 psia (652.93 kPa
absolute), 0.684 lbs. of TCE is in equilibrium in a liquid solution
with 0.316 lbs. 0.143 kg) of R.sub.22. At 40.degree. F.
(4.44.degree. C.) and 24.7 psia, (170.30 kPa absolute) 0.262 lbs.
(0.119 kg) of R.sub.22 vaporizes, leaving 0.054 lbs. (0.024 kg) of
R.sub.22 remaining in solution. Enthalpy measurements indicate the
evolving R.sub.22 absorbs 22.65 Btu (23.88 k-J) as a gross
refrigerating effect in the evaporator.
Assuming perfect heat exchange and equal exit temperatures of
69.6.degree. F. (20.89.degree. C.), the remaining 0.054 lbs. (0.024
kg) of R.sub.22 should vaporize in the economizer as the solvent
entering in at 40.degree. F. (4.44.degree. C.) flows countercurrent
to the incoming refrigerant laden solution streams in lines 15 and
25. The exit temperature is approximately 71.degree. F.
(21.11.degree. C.).
The 0.684 lbs. (0.310 kg) of TCE, with a specific heat of 0.258,
enters the compressor at 70.93.degree. F. (21.63.degree. C.), and
the entering temperature of the 0.316 lbs. (0.163 kg) of R.sub.22
including warmer than 40.degree. F. (4.44.degree. C.) gas from the
economizing zone is calculated as 42.62.degree. F. (5.90.degree.
C.). Isentropic compression of the gas alone would give a discharge
temperature of 148.degree. F. (64.44.degree. C.), so that the
discharge temperature of the liquid and gas is 100.51.degree. F.
(38.06.degree. C.). It is believed that the passage of the R.sub.22
and the TCE through any practical, modern compressor occurs so
rapidly that no significant dissolving of the R.sub.22 in the TCE
occurs.
The value of n, the constant of polytropic compression is
determined from ##EQU1## where T.sub.1 =502.62.degree. R, T.sub.2
=560.51.degree. R, P.sub.1 =24.7.times.144 psf and P.sub.2
=94.7.times.144 psf. n=1.09.
The work of compression in Btu, (P.sub.2 V.sub.2 -P.sub.1
V.sub.1)/J(1-n), is 2.05 Btu (21.61 kJ) per 0.316 lb (0.143 kg)
R.sub.22 vaporized. V.sub.1 and V.sub.2 are taken from the
superheat tables of [American Society of Heating, Refrigerating and
Air Conditioning Engineers, Thermodynamic Properties of
Refrigerants, 1980]. The density of the stripped TCE leaving the
economizer 26 is 3.98 lb/ft.sup.3 (1345.22 kg per m.sup.3), the
pressure head across the 70 psi (482.63 kPa) differential is 120.42
ft. (36.70 m), and the Btu (kJ) of pumping 0.684 lb (0.310 kg) of
TCE is 0.106 (0.112). Hence the total work of compressing the gas
and pumping the liquid is 2.16 Btu/lb (5.02 J per g) of
mixture.
Since the refrigerant-solvent solution, with a specific heat of
0.264 must be subcooled 30.93.degree. (-0.59.degree. ), to
40.degree. (4.44.degree. ) in the evaporator, the net available
refrigerating effect, per pound of gas-liquid circulating mass is
14.48 Btu.
The coefficient of performance of the cycle is thus 6.71. Since the
theoretical coefficient of performance of the pure R.sub.22 cycle
at these conditions is 5.75, the embodiment shown in FIG. 4 is
believed to represent a 16.7% more efficient process than a
comparable vapor compression refrigeration cycle.
Schematically diagrammed in FIG. 5 is another embodiment. A
solvent-liquid refrigerant stream is passed via line 25 to
evaporator 10. As essentially discussed in conjunction with
embodiments above, the refrigerant and solvent of the
solvent-liquified refrigerant stream exhibit negative deviations
from Raoult's Law. Likewise, the pressure over the
solvent-liquified refrigerant stream is reduced, by pressure
reducing valve 16, to allow refrigerant to vaporize and separate
from the solvent in evaporator 10. The evolving mixture is placed,
in the evaporator, in heat exchange relation with a working medium
from which it removes heat. As a result, there are formed a solvent
stream, which passes via line 24, and a refrigerant stream
including gaseous refrigerant, which passes via line 18, exiting
evaporator 10.
It is believed that the solvent stream passing via line 24 may
contain a material portion of refrigerant without hindering
efficiency of the process. More particularly, the solvent stream
leaving the evaporator 10 and passing via line 24 is placed in heat
exchange relation with the solvent-refrigerant stream passing to
the evaporator via lines 15 and 25. Further, the solvent stream in
line 24 is placed in fluid communication with the refrigerant
stream of line 18 such that gaseous refrigerant evolving from the
solvent stream 24 may pass via line 92 to refrigerant stream 18.
This evolution of gas tends to cool the solvent stream, thus
facilitating heat transfer in the economizer or economizing zone
26. This in turn increases the temperature drop, over what might
otherwise be expected, in the solvent-liquified refrigerant stream
as it passes through the economizing zone, and hence increases the
available refrigerating effect in the evaporator.
The refrigerant stream is carried via line 18, as augmented by flow
from line 92, to compressor 88. In the compressor, the gaseous
refrigerant is pressurized sufficiently to dissolve into the
solvent stream in the mixing zone or mixer 11 at the operating
temperature of the mixer, while concurrently giving up heats of
vaporization and of mixing to a working medium placed in heat
exchange relation with the combined refrigerant and solvent
streams. The pressurized gaseous refrigerant is passed from
compressor 88 via line 91 to mixer 11.
The solvent stream, stripped of a substantial portion of its
remaining dissolved refrigerant in the economizer 26, and, having
passed that portion of refrigerant mass to the refrigerant stream
via line 92, is put in heat exchange relation with the refrigerant
gas being compressed in the compressing zone 87. Heat exchange in
compressing zone 87 may be accomplished by substantially enclosing
compressor 88 in a cooling jacket through which the solvent stream,
line 24, flows. It is believed that, by cooling the compression of
the gaseous refrigerant with the solvent stream from the
economizer, polytropic rather than isentropic compression occurs,
resulting in a reduced work of compression and improved cycle
efficiency.
From compressing zone 87, the solvent stream passes via line 93 to
solvent pump 13 wherein it is raised in pressure to a level as
nearly as possible equaling that of the pressurized gaseous
refrigerant in line 91.
It is believed that the temperature of the solvent stream exiting
the solvent pump in line 94 will generally be less than, or at most
equal to, that of the solvent-liquified refrigerant solution in
line 15. Hence, the solvent stream in line 94 is put in heat
exchange relation, in heat exchanger or precooler 86, with the
solvent-liquified refrigerant solution stream of line 15. The
purpose of the heat exchange is to subcool the solution stream
leaving the mixer 11 and thus to increase the available
refrigerating effect in the evaporator.
The compressed gaseous refrigerant stream of line 91 and the pumped
solvent stream of line 94 meet and are mixed in mixing zone or
mixer 11. The mass of gaseous refrigerant and the mass of liquid
solvent combine to form a liquified refrigerant-solvent solution in
the mixer. The heats of condensation and of mixing released in the
formation of this solution are then transferred to a working medium
with which the refrigerant and solvent masses are in heat exchange
relation.
The circulating refrigerant-solvent solution then passes in line 15
through heat exchangers 86 and 26, being subcooled at each stage,
to pressure-reducing valve 16 and evaporator 10. The flow process
is then repeated.
By way of example for this embodiment, a refrigerant-solvent
combination of R.sub.22 -trichloroethane (TCE) might be employed.
The operation of the embodiment indicated in FIG. 5 is highlighted
by the various temperatures shown in the drawing, all of which are
in degrees Fahrenheit. It is presumed that a cycle using R.sub.22
as refrigerant and TCE as a solvent was employed. As in the case of
the embodiment pictured in FIG. 4, cycle calculations are based on
one pound of circulating mass, with mixer temperature and pressure
of 110.degree. F. and 94.7 psia, respectively, and evaporator
temperature and pressure of 40.degree. F. and 24.7 psia,
respectively.
At mixer conditions, 0.684 lb of TCE is in equilibrium in a liquid
solution with 0.316 lb of R.sub.22. At evaporator conditions, 0.262
lb of R.sub.22 vaporizes from the original pound of solution.
Enthalpy measurements indicate the evolving R.sub.22 absorbs 22.65
Btu as gross refrigerating effect in the evaporator.
Assuming perfect heat exchange and equal exit temperatures of
72.2.degree. F., substantially all of the remaining 0.054 lb of
R.sub.22 should vaporize in the economizer 26 as the solvent
entering at 40.0.degree. flows countercurrent to the incoming
refrigerant-laden solution stream in line 15. The exit temperature
from economizer 26 is 72.2.degree. F., due in part to the evolution
of refrigerant gas from the solvent stream of line 24. The 0.684 lb
of TCE, with a specific heat of 0.258, enters heat
exchanger-cooling jacket 87 at 70.9.degree., and the entering
temperature of the 0.262 lb of R.sub.22, including warmer than
40.degree. gas from the economizing zone, is calculated as
42.7.degree. F. Isentropic compression of the gas in compression
zone 88 would give a discharge temperature of 148.degree. F., so
that the discharge temperature of the polytropically compressed gas
in line 91 and heated solvent exiting the cooling jacket in line 93
is 99.8.degree. F. The value of n, the constant of polytropic
compression, is determined from: ##EQU2## Where T.sub.1
=502.735.degree. R, T.sub.2 =559.813.degree. R, P.sub.1
=24.7.times.144 psfa and P.sub.2 =94.7.times.144 psfa, the number
n=1.087.
The work of compression in Btu, ##EQU3## is 2.00 per 0.316 lb of
R.sub.22 vaporized. (Reference values of V.sub.1, V.sub.2, etc.,
are as previously cited.)
The density of the stripped TCE leaving economizer 26 is 83.98
lb/ft.sup.3, the pressure head across the 70 psi pressure
differential is 120.42 ft and the Btu of pumping, via solvent pump
13, the 0.684 lb of TCE is 0.106. Hence the total work of
compressing the gas and pumping the liquid is 2.11 Btu/lb of
solution.
The 0.684 lb of TCE at 100.5.degree. F. next flows from solvent
pump 13, via line 94 to heat exchanger-precooler 86, where it is
put in countercurrent heat exchange relation with one pound of
solution at 110.degree. F., and having a specific heat of 0.264.
The exit temperature of both streams is 106.8.degree. F.
Since the temperature of the refrigerant-solvent solution, in line
15, at the entrance to the economizer has been reduced, a new exit
temperature for the solvent stream, line 24, and the solution
stream, line 25, is calculated as 70.3.degree. F.
Subcooling to 40.degree. F. at the pressure reducing or throttling
valve 16 by vaporizing refrigerant leaves 14.38 Btu per pound of
solution as net refrigerating effect in the evaporator 10. The
coefficient of performance, 14.38/2.11 is 6.82.
A number of variations and substitutions to the embodiments shown
in the drawing are possible. By way of example, it is believed that
the embodiment in FIG. 1 may be operated such that a portion of the
solvent from line 19 may be sprayed into the refrigerant stream in
line 18 and so permit a centrifugal compressor to develop higher
pressures, since the pressure developed by a centrifugal pump is
proportional to the product of density of the medium being handled
and the square of the tip speed. Thus, much greater pressures can
be developed for a given centrifugal pump such that a smaller pump
may be used.
In another variation on the embodiment shown in FIG. 1, the pump
type compressor 12 may be replaced with a jet compressor. Thus, a
high velocity liquid jet of solvent supplied to the jet compressor
by a portion of the solvent from line 19 may be used to compress
the refrigerant gas coming from the evaporator-effervescer 10. The
presence of a higher specific heat solvent is believed to result in
more efficient compression, due to the greater heat capacity of a
liquid. More particularly, the compression becomes more nearly
isothermal, hence more efficient.
In another embodiment, the compressor 12 and solvent pump 13 may
both be replaced by a liquid ring compressor which compresses the
refrigerant gas, circulates the solvent and initiates mixing of gas
and solvent prior to entry into mixer 11 through a single conduit.
Compression is understood to be more nearly isothermal and hence
more efficient.
For example, as shown in FIG. 1, valve 76 may be closed off and
valve 71 and liquid ring compressor 77 operated such that both
solvent and refrigerant pass from evaporator 10 via line 72 to ring
compressor 77. The compressed mixture would then pass to mixer 11.
By way of example, the ring compressor 77 might be a double lobe
compressor manufactured by Nash Engineering Co. of South Norwalk,
Conn. and described in that company's Bulletin No. 474-C dated
1971.
In yet another embodiment, the refrigerant may be foamed with the
solvent and solvent pump 13 could be eliminated from the embodiment
shown in FIG. 1. Both refrigerant and solvent would be circulated
from evaporator 10 to the compressor 12 and hence to mixer 11.
Similarly, the embodiment shown in FIG. 2 may also be modified. For
example, the solvent pump 13 may be replaced with a device to
inject the compressed refrigerant gas from conduit 14 into the
solvent stream in conduit 24, thus propelling both refrigerant gas
and solvent liquid to condenser-mixer 11. Also, as shown in FIG. 1,
valves 71 and 74 may be operated so as to allow at least a portion
of solvent to bypass solvent pump 13 while valve 74 is operated to
allow a sufficient amount of vapor to pass from line 14 into line
72 via line 73.
The present invention may also be used in conjunction with other
systems. For example, a generator-absorber pair might be hooked up
in tandem with the compressor to provide a back-up for the same.
The generator could function off a secondary source of heat, such
as from an exhaust, or a form of solar energy. For example, as
shown in FIG. 2, valves 41 and 42 could be placed on both sides of
compressor 12 in lines 18 and 14 to hook a generator-absorber pair
48, 44 into the system. A portion of the vaporized refrigerant
could then pass from line 18 via line 43 to the absorber, absorbed
in an appropriate secondary solvent and then be pumped in solution
by pump 46 through lines 45 and 47 to the generator 48. Upon
evaporation of the refrigerant in the generator 48 the now
compressed vapor could be passed via line 49, valve 42 and line 14
to the mixer 11, while secondary solvent was returned to the
absorber 44, via line 50.
The secondary solvent may be the same as used in the primary
system.
Of course, in order to obtain all of the advantages of the present
invention, the generator-absorber pair should not be completely
substituted for the compressor 12. Rather, the generator-absorber
pair and the mechanical compressor are complementary means of
generating pressurized refrigerant gas.
Further, with respect to the FIG. 4 embodiment, as would be known
to one skilled in the art having the benefit of this disclosure,
there exist a number of alternatives for concurrent
compression-pumping of the gas and liquid constituents. For
example, large multi-stage centrifugal compressors as manufactured
by York, frequently are designed to inject liquid refrigerant into
the vapor stream as a substitute for flash intercooling between
stages. However, in such a case, the liquid flow rate should be as
reasonably uniform as possible. Also, helical or rotary screw
compressors, such as manufactured by Dunham-Bush may be adapted for
use with the chemically assisted mechanical refrigeration system as
disclosed herein. However, in the chemically assisted mechanical
refrigeration system, the solvent should preferably serve as a
coolant, lubricant and sealant. Further, bulky oil separators and
oil coolers should be eliminated since the solvent passes on to the
mixer with the compressed gas.
For smaller capacities, the Wankel-type compressor, manufactured by
Ogura Clutch of Japan, or the rolling piston compressors of Rotorex
(Fedders) and Mitsubishi may prove useful. Possibly useful also is
the multistage centrifugal compressor-pump of the type manufactured
by Sihi. In this device, a gas-liquid mixture enters a first,
closed impeller axially and the denser liquid is thrown to the
periphery. The lighter gas is ported off to the second and
subsequent stages nearer the center of the chamber and both gas and
liquid are then carried together through second and subsequent
impeller stages.
Alternately, where an economizer is used and where capital costs
permit, a turbine may be installed in the refrigerant-solvent
stream between the economizer and evaporator to function as a
pressure reducing device, supplementing throttling devices. Under
appropriate operating conditions, it is believed that a subcooled
stream exiting the economizer is least likely to flash refrigerant
gas at this point and the resultant shaft work may be used to power
booster pumps, compressors for the system, auxiliary fans or the
like.
Additional items of equipment may be employed within the framework
of the present invention. For example, control of the system as
well as system versatility may be enhanced through the use of
appropriate process controls, though the use of essentially manual
control devices may suffice for many operations. Additionally, in
the embodiment shown in FIG. 4, a low pressure drop mixing of
gaseous refrigerant and liquid could be achieved by using an inline
motionless mixer such as one offered by the Mixing Equipment Co.,
Inc. of Avon, N.Y.
Further modifications and alternative embodiments of the apparatus
and method of this invention will be apparent to those skilled in
the art in view of this description. Accordingly, this description
is to be construed as illustrative only and is for the purpose of
teaching those skilled in the art the manner of carrying out the
invention. It is to be understood that the forms of the invention
herewith shown and described are to be taken as the presently
preferred embodiments. Various changes may be made in the size,
shape and arrangement of parts. For example, equivalent elements or
materials may be substituted for those illustrated and described
herein, parts may be reversed, and certain features of the
invention may be utilized independently of the use of other
features. All this would be apparent to one skilled in the art
after having the benefit of this description of the invention.
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